<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>图案生成-随机效果</title>
    <style>
        canvas{
            border: 1px solid #ccc;
        }
    </style>
</head>
<body>
    <canvas width="512" height="512"></canvas>

    <script src="/common/lib/gl-renderer.js"></script>
    <script type="module">
        /**
         * gl-renderer用法
         * 1.创建renderer对象
         * 2.创建webgl程序
         * 3.设置uniform变量
         * 4.设置缓冲区数据
         * 5.渲染
         * 
         * */ 

        //  1.
         const canvas = document.querySelector("canvas");
         const renderer = new GlRenderer(canvas);

        // 2.
        const vertex = `
            attribute vec2 a_vertexPosition;
            attribute vec2 uv;
            varying vec2 vUv;
            
            void main() {
                gl_PointSize = 1.0;
                vUv = uv;
                gl_Position = vec4(a_vertexPosition, 1, 1);
            }
        `;
        const fragment = `
            #ifdef GL_ES
                precision mediump float;
            #endif

            varying vec2 vUv;

            uniform float uTime;

            // 随机数
            float random(vec2 st){
                return fract(sin(dot(st.xy, vec2(12.9898, 78.233))) * 43758.5453123);
            }
            
            void main() {
                vec2 st = vUv * vec2(50.0, 50.0);

                st.x -= random(vec2(floor(st.y))) * uTime;

                vec2 f = fract(st);
                vec2 l = floor(st);

                // 计算y方向的间隔
                float y = step(0.2, f.y);

                float x = random(l);
                float d = step(0.3, x);

                gl_FragColor.rgb = vec3(y * d);
                gl_FragColor.a = 1.0;
            }
        `;

        const program = renderer.compileSync(fragment, vertex);
        renderer.useProgram(program);

        // 3.
        renderer.uniforms.uTime = 0;

        // 4.
        renderer.setMeshData([{
            positions:[
                [-1, -1],
                [-1, 1],
                [1, 1],
                [1, -1],
            ],
            attributes:{
                uv:[
                    [0, 0],
                    [0, 1],
                    [1, 1],
                    [1, 0],
                ]
            },
            cells: [[0, 1, 2], [2, 0, 3]],
        }]);

        // 5.
        renderer.render();

        function update(t){
            renderer.uniforms.uTime = t * 0.01;

            requestAnimationFrame(update);
        }
        requestAnimationFrame(update);
    </script>
</body>
</html>